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Q: TPS3306 - Failure by 734151
I connected the TPS3306 VDD to 3.3V but I am monitoring 5V so the SENSE1 pin is connected to 5V. This connection results in a TPS3306 failure when I apply power. I supsect the protection diode on the sense pin connects the input to the supply causing the distruction of the device.
In order to avoid a PCB revision I need to know the values (typical) of the resistors R1/2/3/4 of the internal resistor divider in order to use a TPS3306-25 with series resistors on the SENSE1 and SENSE2 pins. Thank you
A: Re: TPS3306 - Failure by 10449
You are correct that applying 5V to the SENSE1 or SENSE2 pins with 3.3V applied to VDD will damage the IC. This condition exceeds the absolute maximum ratings of the IC. The information you are looking for is indirectly provided by the datasheet. The High Level Input Current for the SENSE1 and SENSE2 pins is defined with SENSE1 and SENSE2 = 6V. The typical input resistance for these two pin are 6V/5uA = 1.2Mohm and 6V/6uA = 1Mohm.
Note that simply adding an external resistor will result in a very wide tolerance on the trip point because the internal resistor values vary by approximately 50%-60%. A more accurate solution is to add two external resistors to create a resistor divider from the 5V bus being monitored to the SENSE1 input pin. You can scale the trip point to any voltage that is higher than the trip point specified at the SENSE1 pin. For example, the TPS3306 -2.5V version trips when SENSE1 goes below 2.93V. Using the resistor dividers described above and making both resistor equal to 10kohm, the TPS3306 still pulls the /RESET pin low when SENSE1 goes below 2.93V, however, because of the resistor divider, the voltage being sensed is at 2.93V*2=5.86V. The sum of the external resistor divider should be approximately 100 times lower than the internal resistor divider. Using higher resistor values reduces trip point accuracy because of the current flowing into SENSE1. Using lower resistor divider values is more accurate but consumes more current from the voltage rail being monitored.
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